Perin is correct. You need to generate LOD. You can read about it in painful detail here -> http://www.truancyfactory.com/tutorials/fallout3/fallout_lod.html. Not sure if it works the same for NV, but that's how it works for FO3. It looks complicated but 90% of it boils down to knowing where the files end up and what folder they need to be in. Let me know how it goes.
TheMagician,
Generating LOD is exactly the same in New Vegas as it was in FO3 so, your tutorial should be just as helpful for both games. I have created some modders resources to try to help people get set up to generate LOD. http://www.fallout3nexus.com/downloads/file.php?id=13676 , http://www.newvegasnexus.com/downloads/file.php?id=36693 both contain most if not all files needed to generate LOD in there correct file path. I've even converted all the textures to TGA and, created a proper source folder so people wont have to do it themselves.
cev